What is nasal air emission? | David J. Zajac, PhD, CCC-SLP

Nasal air emission is an obligatory symptom of incomplete velopharyngeal (VP) closure during production of stop, fricative, and/or affricate consonants. All of these consonants are produced with relatively high intraoral air pressure and require complete closure of the VP port. If there is incomplete VP closure — that may occur in a child with repaired cleft palate — then air will escape into the nasal cavity and may become audible. Factors that determine if nasal air escape will become audible include effort level (loudness), size of the VP opening, and resistance of the nasal passage. There are three generally recognized types of nasal air emission as reviewed below.

Visible only. If a small mirror (or detail reflector) is held under the nostrils of a child saying “pah pah pah”, fogging on the mirror indicates that VP closure is incomplete (see Figure 1 below). Typically, speech-language pathologists (SLPs) will test a number of syllables that target the /p/ and /s/ consonants as these sounds require complete VP closure. If there is fogging but no audible noise, then airflow is moving relatively unimpeded through the nasal cavity (i.e., laminar or smooth flow). This type of inaudible nasal air emission does not require any treatment.

Figure 1. Method to detect visible nasal air escape during speech.

Audible nasal emission. This type of nasal air emission has a relatively quiet, hissing-like sound that accompanies the production of the target consonant. You can simulate this type of noise by forcibly exhaling through the nose with your lips closed (Peterson-Falzone et al., 2010). Under this condition, the soft palate is relaxed (VP port completely open) and airflow becomes turbulent as it passes through and exits the nose. To become audible, airflow needs to encounter some type of resistance (constriction) in the nose. Typically, this will be the nasal valve, the smallest cross section of the nasal passage located near the exit of the nose.

Audible nasal emission is usually associated with a relatively large VP gap (Kummer et al., 1992). The large VP gap allows airflow to remain mostly laminar until it reaches the nasal valve. Children who exhibit audible nasal emission are also typically quite hypernasal on vowels and other voiced consonants, due to a large VP gap. In such cases, the hypernasality is typically more perceptually salient than the audible nasal air emission. An audio sample and spectrogram of a child with hypernasality and audible nasal emission is shown below. As seen in the spectrogram, audible nasal emission occurs as relatively high-frequency aperiodic energy during the stop segments, consistent with turbulent airflow.

Audio sample of a young girl with repaired cleft palate saying the syllable string /pi pi pi/. There is hypernasality associated with the vowels and audible nasal air emission associated with the /p/ segments.

Figure 2. Waveform (top) and spectrogram (bottom) of above speech sample. Ovals highlight aperiodic noise in higher frequencies during the second and third stop gaps of /p/. This noise is caused by turbulent airflow as it escapes from the nose.

Audio sample of just the second stop gap of the above sample. The relatively quiet aperiodic noise has an /s/-like quality.

Audible nasal turbulence (aka rustle). Audible nasal turbulence has a relatively loud, snorting-like quality. Although difficult to simulate, the sound is similar to a raspberry produced with the lips. Indeed, you can think of this sound as a velar raspberry. Unlike audible nasal emission, Zajac and Preisser (2016) showed that nasal turbulence is characterized primarily by low-frequency periodic noise in a spectrogram. Peterson-Falzone et al. (2010) attribute this noise to either tissue vibration (flutter) and/or displacement of mucous in the VP gap. Audible nasal turbulence is usually associated with a relatively small VP gap (Kummer et al., 1992). A small VP gap causes airflow to become turbulent before reaching the exit of the nose. More importantly, a small VP gap also allows vibration (flutter) of tissue, an aerodynamic-myoelastic event. In essence, the physiology underlying audible nasal turbulence is quite similar to the mechanism that causes vocal-fold vibration. As noted by Peterson-Falzone et al. (2010), audible nasal turbulence is perceptually more severe than audible nasal emission because it is relatively louder and more distinctive. Below is an audio sample and spectrogram of a child who exhibits audible nasal turbulence.

Audio sample of a young girl with repaired cleft palate saying the syllable string /pi pi pi/. There is distinctive audible nasal turbulence associated with the /p/ segments.

Figure 3. Waveform (top) and spectrogram (bottom) of the above speech sample. As indicated in the spectrogram, flutter noise occurs during the second and third stop gaps of /p/. The noise is characterized by periodic vertical striations that extend from the low to high frequencies. This type of noise is caused by vibration of either tissue and/or mucous in the velopharynx.

Audio sample of just the second stop gap of the above sample. The relatively loud periodic noise has a flutter or raspberry-like quality.

What is the source of audible nasal turbulence?

As indicated above, Peterson-Falzone et al. (2010) hypothesized that either tissue vibration or displacement of mucous in the VP port could cause nasal turbulence. As shown in the spectrogram in Figure 3, there is clear evidence of periodic noise, indicating that something is vibrating. That ‘something’ is most likely velar tissue but the possibility of adenoid (or other) tissue cannot be ruled out for a given speaker. Below are two nasoendoscopic videos that show flutter of velar tissue. Both videos are from a speaker with repaired cleft palate who underwent sphincter pharyngoplasty. The first video shows the speaker saying the word “see” three times. There is flutter of posterior velar tissue during production of each /s/ segment, especially the first /s/. The second video is from the same speaker and shows an isolated, and longer, instance of velar flutter.

see see see

Isolated flutter

References

Kummer, A. W., Curtis, C., Wiggs, M., Lee, L., & Strife, J. L. (1992). Comparison of velopharyngeal gap size in patients with hypernasality, hypernasality and nasal emission, or nasal turbulence (rustle) as the primary speech characteristic. The Cleft palate-craniofacial journal, 29(2), 152-156.

McWilliams, B. J., Morris, H. L., & Shelton, R. L. (1990). Cleft palate speech. Mosby Elsevier Health Science.

Peterson-Falzone , SJ , Hardin-Jones , MA , & Karnell , MP (2010). Cleft palate speech . St. Louis St. Louis, MO: Mosby.

Zajac, D.J., & Preisser, J. (2016). Age and phonetic influences on velar flutter as a component of nasal turbulence in children with repaired cleft palate. Cleft Palate-Craniofacial Journal, 53(6):649-656.